J.M. del Valle

Caking phenomena in amorphous food powders

Abstract Caking of free-flowing powders during storage is a deleterious phenomenon that is ubiquitous in the feed, fertilizer and pharmaceutical industries, and of economical importance for low-moisture foods. Among other subjects related to caking of amorphous powders, the following aspects are reviewed in this article: (1) physical and morphological changes, and quantitative procedures to assess caking; (2) proposed mechanisms of caking phenomena; (3) examples of caking in food materials; (4) the relationships between storage-induced caking and other phenomena and the glass transition of amorphous powders; (5) methods for estimating the evolution of caking with time from the physical properties of powder samples and environmental conditions; and (6) measures to minimize the occurrence of caking phenomena.

Glass transitions and shrinkage during drying and storage of osmosed apple pieces

Abstract The relationship between shrinkage during drying and ‘glass’–‘rubber’ transitions of apple tissue was studied. Our results did not indicate that structural collapse of apple pieces can be reduced by diminishing the difference Δ T between drying temperature and glass transition temperature ( T g ) of the fruit matrix. Apple shrinkage was not consistently depressed by reducing drying temperature, infusing larger amounts of T g -depressing agents (sucrose, maltose, lactose) or infusing similar amounts of solutes with higher anhydrous T g s. However, sugars added during osmotic dehydration pretreatments help decreasing structural collapse during subsequent air drying, which was reflected by a 20–65% increase in final volume of samples treated with 50% sucrose and maltose solutions as compared to an air-dried, control sample. Dried samples remained in the “rubbery” state after drying and shrunk during subsequent storage.

Revision: Extracción con CO2 a alta presión. Fundamentos y aplicaciones en la industria de alimentos / Review: High pressure CO2 extraction. Fundamentals and applications in the food industry

Supercritical extraction (SFE) is a unit operation that exploits the dissolving power of supercritical fluids (SF) under conditions above their critical temperature and pressure. It is possible to obtain solvent-free extracts using SF and the extraction is faster than using conventional organic solvents. These advantages are due to the high volatility of SF (gases under normal environmental conditions) and improved transport properties (i.e., high diffusivity and low viscosity). When using carbon diox ide (CO,) in particular, moderate-temperature processing and high selectivity towards valuable microconstituents in natural products can be achieved. This article presents a review of transport properties and solubilities in SF, particularly CO2, as well as other underlying factors that are respon sible for the kinetics and phase equilibrium in SFE processes. It also describes the selective CO 2 ex traction of essential oils, pungent principles, carotenoid pigments, antioxidants, antimicrobials, and related substances to be used as ingredients for the food, drug and perfume industries, from spices, herbs and other plant materials. These very important applications are discussed from the point of view of the potential applications of SFE in Latin America. The two most important commercial ap plications of SFE in the food industry, namely hop extraction and coffee decaffeination, are reviewed to a limited extent. Some other potential applications briefly described include extraction and frac tionation of edible fats and oils, purification of solid matrices, and concentration of fermentation broths, fruit juices and other extracts. In most cases CO2 extracts are compared with counterparts obtained using conventional methods.

Differential scanning calorimetry of low-moisture apple products

Abstract Differential scanning calorimetry (DSC) was used to detect thermal phase transitions in low-moisture apple products, cell walls and related materials. Freeze-dried (FD) apple tissue equilibrated over P 2 O 5 exhibited a T g around 11°C, similar to that of FD apple juice and slightly higher than the predicted value for the sugar mixture in juice (7°C). Samples also showed an endothermic peak around 50–70°C. Cell wall (CW) material from apple prepared by five different methods and dried over P 2 O 5 showed an endothermic peak (onset around 120°C and peak between 130–160°C) caused by water evaporation. No glass transition was detected in CW preparations for any water activity. The same behavior was observed for microcrystalline cellulose, apple pectin, pine wood and walnut leaves equilibrated over P 2 O 5 . Low-moisture CW exhibited a more hydrophobic behavior than apple tissue as revealed by adsorption isotherms.

Volumetric procedure to assess infiltration kinetics and porosity of fruits by applying a vacuum pulse

Abstract In this work an improved ‘volumetric’ procedure was developed to assess fruit porosity using a hydrodynamic mechanism, to replace the ‘gravimetric’ alternative proposed by Fito in 1994. This procedure also facilitated study of the kinetics of liquid infiltration in fruit pieces as a result of the application of a vacuum pulse. It was observed that apparent porosity increased as the absolute pressure of the vacuum pulse decreased, probably as a result of tissue damage or deformation-relaxation phenomena. In the case of apples, porosity increased from an initial value of about 0.20 to about 0.30, and this increase took place in a relatively short period (about 1 min after vacuum rupture). These values did not appear to be significantly (P

Comparision of conventional and supercritical CO2-extracted rosehip oil

Supercritical CO2 (SCO2) can be utilized to extract oils from a number of plant materials as a nontoxic alternative to hexane, and there is industrial interest in using SCO2 extraction to obtain high-quality oils for cosmetics and other high-value applications. A possible substrate is rosehip (Rosa aff. rubiginosa) seed. The scope of our work was to select SCO2 extraction conditions and to compare cold-pressed, hexane-extracted and SCO2-extracted rosehip oil. We used a fractional factorial experimental design with extraction temperature (T, 40-60 °C), extraction pressure (p, 300-500 bar) and dynamic extraction time (t, 90-270 min) as independent variables and yield and color as response variables. Samples of 100 g flaked rosehip seeds were extracted with 21 g CO2/min, following a static extraction (15 min adjustment) period. Resulting data were analyzed using response surface methodology. Extracted oil (4.7-7.1% in our experimental region) increased slightly with p and more pronouncedly with T and specially t. On the other hand, the photometric color index was independent of t but worsened (increased) as a result of an increase in either p or specially T. We extracted five batches of 250 g seeds with 21 g CO2/min at 40 °C and 300 bar for 270 min and compared the oil with samples obtained by solvent extraction (a batch of 2.5 kg of laminated seeds was treated with 10 L hexane and rotaevaporated until there was virtually no residual hexane) and cold pressing, by determining color, fatty acid composition, iodine index and saponification index. It was concluded that SCO2 allows an almost complete recovery of rosehip oil (6.5% yield), which is of a better quality than the oil extracted with hexane. Yield was higher than it was when using a cold-pressing process (5.0% yield).

Extraction of oil and minor lipids from cold-press rapeseed cake with supercritical CO2

This study examines the extraction of oil from cold-press rapeseed cake using Supercritical CO2(SC-CO2). The effects of pressure (20, 30, and 40 MPa), temperature (40, 50, and 60 oC), and extraction time (60, 90, and 120 min) on oil yield and composition (tocopherols and carotenoids) were studied using response surface design. The results indicated that pressure influenced the most the yield of oil, followed by temperature and extraction time. Extraction time had no effect on oil composition. Extraction pressure and temperature did not affect the tocopherol concentration of the oil to a great extent, whereas temperature had no affect in its carotenoid concentration. A comparison was made between the relative qualities of oil extracted with SC-CO2at 40 MPa and 60 oC and with n-hexane. Neither solvent affected the unsaponifiable matter content or the composition of phytosterols (mainly β-sitosterol, campesterol and brassicasterol) of the oils, although there was a significant difference (p<0.05) in tocopherol. Extraction with SC-CO2at 40 MPa and 60 oC is recommended to obtain rapeseed-oil enriched with tocopherols and carotenoids as important functional components.